X-ray producing devices are extremely effective and valuable tools that are used in a wide variety of industrial and medical applications. While used in a number of different applications, the basic operation of these devices is similar.
Generally speaking, x-rays are produced when electrons are accelerated and then impinged upon a material of a particular composition. This process is typically carried out within a vacuum enclosure formed as part of the x-ray producing device. Disposed within the evacuated enclosure is an electron generator (i.e., cathode), and an anode, which is spaced apart from the cathode. In operation, electrical power is applied to a filament portion of the cathode, causing electrons to be emitted. A high voltage potential is placed between the cathode and the anode, causing the emitted electrons to accelerate towards a target surface on the anode. Typically, the electrons are “focused” into an electron beam towards a desired “focal spot” located on the target surface.
During operation of the x-ray producing device, the electrons in the beam strike the target surface at a high velocity. The target surface on the target anode is composed of a material having a high atomic number, and a small portion of the kinetic energy of the striking electron stream is thus converted to x-rays, which are electromagnetic waves of very high frequency. The resulting x-rays, which emanate from the target surface in all directions, are blocked using heavy metal shielding and collimated through a window formed in the shielding for penetration into an object.
By way of the present invention, it has been discovered that the amount of heavy metal shielding used in radiation sources such as x-ray producing devices may be reduced by placing the radiation producing target closer to and substantially in the center of shielding adopting, for example, a spherical or substantially spherical geometry. The relocation of the target in these sources or devices is made possible by the use of a vacuum drift tube.
The present invention therefore generally provides a method for reducing the amount of shielding used in radiation sources such as x-ray producing devices, which basically comprises: placing a radiation producing target at the end of a vacuum drift tube and substantially in the center of a shield for blocking radiation emitted from the target.
The present invention further generally provides a radiation source such as an x-ray producing device, which basically comprises: a vacuum drift tube; a radiation producing target; and a shield for blocking radiation emitted from the radiation producing target, wherein the radiation producing target is located at the end of the drift tube and substantially in the center of the shield.
The present invention more particularly provides an improved x-ray producing device, which comprises:                (1) an electron accelerator structure defining an electron flow path and having an electron injection end and an electron exit end;        (2) an electron gun having an electron source, which is located at the injection end of the electron accelerator structure, for producing and delivering a stream of electrons to the accelerator structure;        (3) a vacuum drift tube having a first end and a second end, wherein the first end of the drift tube is located at the electron exit end of the accelerator structure;        (4) a target located at the second end of the vacuum drift tube for producing x-rays from electrons striking a surface of the target; and        (5) a shield located around the drift tube for blocking x-rays emitted from the target, wherein the shield has one or more openings for forming an x-ray beam having a pre-selected cross section from the x-rays emitted from the target,        wherein, the target is located substantially at the center of the shield.        
The present invention further provides a radiation (e.g., x-ray) inspection or imaging system that employs the radiation source described above. The inventive system is a lighter weight system and thus particularly advantageous for portable or mobile system applications.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.